This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Bolus PWI Measurement Of Quantitative CBF Can Be Improved Using An Arterial Spin Label Derived Scaling Factor: A Comparative Xenon CT Study Bolus dynamic susceptibility contrast (DSC) perfusion-weighted imaging (PWI) and arterial spin labeling (ASL) are two methods of measuring cerebral blood flow (CBF) using MRI. Each has different strengths and weaknesses. ASL CBF levels are reliable in high flow regions, but suffer from errors and low SNR in regions with long arterial arrival times. PWI, particularly when using delay-invariant deconvolution, is in theory unaffected by long arrival times. However, absolute quantitation is challenging, due to uncertainties in AIF &VOF partial volume and the nonlinear relationship between transverse relaxivity and contrast concentration. This study describes a method that uses ASL CBF measurements in regions with short transit delays (as measured by Tmax) to scale PWI CBF measurements. Stable xenon CT was used as a gold standard for CBF. To read about other projects ongoing at the Lucas Center, please visit http://rsl.stanford.edu/ (Lucas Annual Report and ISMRM 2011 Abstracts)